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Frequently Asked Questions

4. Q: Some manufacturers use the term "synthetic rubber" to describe the materials they use to encapsulate their transformers, for their leads, or for connectors. What does this mean? Does Amerace also use synthetic rubbers?
A: Good question. We suggest that you ask anyone who uses the term "synthetic rubber" to be more specific. As explained in the following, it will help you evaluate how appropriate their technology is. Specifically you will want to know if they are using TPEs, which are today’s material of choice for high quality isolating transformers and cable assemblies.

There are really only two fundamental kinds of rubber, natural rubbers (latex) that come from the sap of rubber trees, and synthetic rubbers, which are made from petroleum. No latex is used in airfield lighting, so in that sense all rubbers used are synthetic, including those of Amerace.

There are a wide variety of synthetic rubbers, and over at least the last 50 years there has been a steady stream of new varieties with better and better properties. So to use only the term "synthetic rubber" isn’t very informative, and might even be termed misleading.

The following is a very brief history of some of the rubbers used in airfield lighting.

Butyl rubbers date from the 1940s, and were used for cables for many years – specifically in what the FAA termed Type A primary cables. They are no longer made and their use will not be permitted when Revision E for the L824 AC is issued.

Polychloroprene/neoprene date from the 1930s, and were used for cable insulation and transformer encapsulation by Amerace from the late 40s to the early 90s.

EPDMs and EPRs date from the early 60s. Amerace uses EPDMs in primary and secondary connector kits.

EPR is used as insulation for some primary field cables.

XLPE (cross-linked polyethylene) dates from the early 60s, and is the most commonly used material for primary field cables in the US and many other areas.

TPEs (thermoplastic elastomers, also called TPRs or TPVs) date from the 1970s, with many new varieties developed over the intervening years. Amerace has used TPEs since the early 90s for primary and secondary cables, for molded connectors, and for transformer encapsulation.

In addition to commercial considerations, the improved properties of new rubber varieties has contributed to the changes in use. For example:

The use of Butyl and Neoprene rubbers has declined sharply because they have relatively low dielectric strength, and they absorb considerable water over time.
EPDMs have high dielectric strength, absorb little water, and have the flexibility required for connector kits.
EPRs have high dielectric strength, and are very flexible, so some users prefer them for field primary cables. They are not mechanically robust however, so they require a jacket.
XLPE has high dielectric strength, and is mechanically very robust, so it does not require a jacket. It has the drawback that it is very stiff.
TPEs have high dielectric strength, low water absorption, and can easily be injected molded and bonded to themselves. This has made them today’s material of choice for high quality isolating transformers and cable assemblies.
For a comparison of some properties of several rubbers, click.